1. Field of the Invention
The present invention relates to a communication apparatus that performs communication through a solid-wire communication line.
2. Description of the Related Art
There is a conventional communication apparatus in which data communication is performed through a solid-wire communication line. As a method for judging 0/1 of data at the time of data communication between an interrogator and a responder, such communication apparatus sets a reference time by a delay circuit to judge a voltage change of a signal faster than the reference time as “0”, and a voltage change of a signal slower than the reference time as “1”, within unit time of data communication. The structure of the conventional communication apparatus will be described hereinafter by referring to the accompanying drawings.
FIG. 6A is a diagram to show the construction of the related art. An interrogator 100A and a responder 100B are connected through a single communication line. The responder 100B comprises a comparator circuit 102, a delay circuit 103, and an output circuit 104. A reference time Tc that is shorter than data communication unit time is set in the delay circuit 103.
First, description is given about the case where the responder 100B receives data. FIG. 6B is a diagram to show a potential of the communication line when the responder 100B receives data in the conventional case. When data is received, the comparator circuit 102 compares voltage change time Tdi of a data signal DI, that is transmitted from the interrogator 100A through the communication line 101 and received by the responder 100B within the data communication unit time, with the reference time Tc set by the delay circuit 103. It is judged as data “0” When voltage change is generated in the data signal DI in a shorter time than the reference time Tc. In the meantime, the data signal DI is judged as data “1” when there is voltage change generated in the data signal DI in a longer time than the reference time Tc.
Next, description is given to the case where the responder 100B transmits data to the interrogator 100A. FIG. 6C shows the potential of the communication line 101 at the time of data transmission in the conventional case. With respect to the case of data transmission, the data transmitted from the responder 100B to the interrogator 100A through the communication line 101 within unit time of the data communication is explained dividing into the case “0” and the case “1”. When the transmitted data is “0”, a voltage change is given by the output circuit 104 to the data signal DO of the communication line 101 at a time Tdo that is shorter than the reference time Tc. In the meantime, when the transmitted data is “1”, a voltage change is given by the output circuit 104 to the data signal DO of the communication line 101 at the time Tdo that is longer than the reference time Tc. Due to such voltage changes supplied to the data signal DO, the interrogator 100A can identify the data of the data signal DO. Examples for this type of related art are U.S. Pat. No. 5,210,846 and No. 5,398,326.
However, it is necessary to set the reference time and data communication unit time to be long when the reference time is set to identify the data by the delay circuit 103, under consideration of dispersion of a timing at the data input/output and the reference time due to manufacturing temperature, etc. Thus, it is not possible to perform high-rate communication in this case.
Furthermore, for performing data communication through a solid-wire communication line, the signal to control the responder 100B is treated as the data communication signal and transmitted at the same fixed data length as the data signal. Thus, it is necessary to secure the time to recognize the control signal and, also for that, the total data communication time becomes longer.